University of Edinburgh

BSL Physics Glossary - reflecting telescope - definition

In a refracting telescope there are two lenses, an eyepiece lens and the other at the far end of the telescope tube is called the objective lens. The problem with refracting telescopes is that the objective lens needs to move much further out to provide images of distant objects. So with a reflecting telescope the design changed - a shorter telescope. Instead of an objective lens, a concave reflecting mirror is used. Light comes into the telescope and is reflected off the mirror, and then at the focal point it is reflected down to an eyepiece lens. The viewer looks at the image through this eyepiece lens, which is below the main telescope.